I just installed a new (rebuilt) Hitchi carburetor in my EA81. I set the idle at around 950. Every so often the idle will suddenly dip down to 450 or so, stay there for a few minutes and then come back up to 950. Sometimes it occurs when it has been running 5 minutes, other times after a 1/2 hour on the freeway. Occasionally a hearty rev will bring the idle back up to 950, but usually it will just stay down at 450 no matter what I do until it decides to snap out of it and climb back up to 950.

 

It hasn't stalled out on me yet, but I do need to pass smog next month and would rather have a steady highish idle for that.

 

Any ideas about what may be causing it? I replaced the PCV valve when I replaced the carburetor. Could I have a vacuum leak that opens and closes intermittently? I removed and inspected the EGR valve too when I did the PCV valve. It opened and closed correctly when vacuum was applied to it.

 

If anyone else has had this problem on the EA81 please chime in.

Sounds like a vacuum leak to me, or debris in a jet.